'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sun Jul 25 10:41:34 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Wed Oct 17 01:12:26 2001 by John Levon <moz@compsoc.man.ac.uk>
.TH strdup 3 2024-06-15 "Linux man-pages 6.9.1"
.SH NAME
strdup, strndup, strdupa, strndupa \- duplicate a string
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.P
.BI "char *strdup(const char *" s );
.P
.BI "char *strndup(const char " s [. n "], size_t " n );
.BI "char *strdupa(const char *" s );
.BI "char *strndupa(const char " s [. n "], size_t " n );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR strdup ():
.nf
    _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
        || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.P
.BR strndup ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.P
.BR strdupa (),
.BR strndupa ():
.nf
    _GNU_SOURCE
.fi
.SH DESCRIPTION
The
.BR strdup ()
function returns a pointer to a new string which
is a duplicate of the string
.IR s .
Memory for the new string is
obtained with
.BR malloc (3),
and can be freed with
.BR free (3).
.P
The
.BR strndup ()
function is similar, but copies at most
.I n
bytes.
If
.I s
is longer than
.IR n ,
only
.I n
bytes are copied, and a terminating null byte (\[aq]\[rs]0\[aq]) is added.
.P
.BR strdupa ()
and
.BR strndupa ()
are similar, but use
.BR alloca (3)
to allocate the buffer.
.SH RETURN VALUE
On success, the
.BR strdup ()
function returns a pointer to the duplicated
string.
It returns NULL if insufficient memory was available, with
.I errno
set to indicate the error.
.SH ERRORS
.TP
.B ENOMEM
Insufficient memory available to allocate duplicate string.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strdup (),
.BR strndup (),
.BR strdupa (),
.BR strndupa ()
T}	Thread safety	MT-Safe
.TE
.SH STANDARDS
.TP
.BR strdup ()
.TQ
.BR strndup ()
POSIX.1-2008.
.TP
.BR strdupa ()
.TQ
.BR strndupa ()
GNU.
.SH HISTORY
.TP
.BR strdup ()
SVr4, 4.3BSD-Reno, POSIX.1-2001.
.TP
.BR strndup ()
POSIX.1-2008.
.TP
.BR strdupa ()
.TQ
.BR strndupa ()
GNU.
.SH SEE ALSO
.BR alloca (3),
.BR calloc (3),
.BR free (3),
.BR malloc (3),
.BR realloc (3),
.BR string (3),
.BR wcsdup (3)
